First, I confirm that the DIPP tool mentioned by @ctomita works perfectly for my case.

Second, I think that it might be useful to share with people how I use the tool to solve my case example.

Test1.pas

//--------------------------------------
{$IFDEF ONE}
ShowMessage('If ONE was defined');
WriteLn('If ONE was defined');
{$IFDEF ONE_ONE}
ShowMessage('If ONE_ONE was defined');
WriteLn('If ONE_ONE was defined');
{$ENDIF}
{$ELSE}
ShowMessage('If ONE was not defined');
WriteLn('If ONE was not defined');
{$ENDIF}
//--------------------------------------
{$IFNDEF ONE}
ShowMessage('If ONE was not defined');
WriteLn('If ONE was not defined');
{$ELSE}
ShowMessage('If ONE was defined');
WriteLn('If ONE was defined');
{$ENDIF}
//--------------------------------------

To remove the all ONE conditional block from Test1.pas and with an assumption that as if there is a conditional symbol named ZERO currently defined, use this command from the Command Prompt:

dipp -o -c -dZERO -h-ONE "Test1.pas" "Test1_output.pas"

Test1_output.pas

//--------------------------------------
ShowMessage('If ONE was not defined');
WriteLn('If ONE was not defined');
//--------------------------------------
ShowMessage('If ONE was not defined');
WriteLn('If ONE was not defined');
//--------------------------------------

Note that when the -c option is specified, DIPP skips over code enclosed by undefined conditionals, inserts include files depending on defined conditionals. In other words, DIPP treats source codes like the compiler would.